Paper degradation
The natural aging of paper
The damaging degree and speed depends in the one hand on the chemical instability of the materials that constitute the paper and on the other hand on the external factors of degradation as the environment, the storage conditions and the handling. Initially, linen, hemp and cotton rags were used to make paper.
In the middle of 19th century, the use of wooden fibers created an important fall of the paper quality. Those papers are made up of lots of impurities and the fibers used are much shorter than before. The result of this is a greater weakness and a lesser good conservation in time. The new sizing process using alum and rosin as well as the use of chemicals to bleach some paper pastes are also responsible of this instability.
The degradation of papier
Temperature and humidity
High temperature speeds up the unstable materials degradation which are part of the artwork but also in the media. Combined to high humidity, it favours also mold growing. In the opposite, low temperature makes the paper crumbly. A too sudden change in temperature can cause physical degradations like cracks or detachments. Likewise, a too sudden change of humidity causes size variations also leading to cracks, detachments or deformations.Light
Light from sun or lamp
essentially emits two kinds of radiations, both dangerous for artworks :
- Infrared rays : they are present in great quantity in day light, they produce an elevation of temperature and have a drying effect on organic materials, like paper, aging will be then faster.
- Ultraviolet rays : they are present in great quantity in light produced by halogen and fluorescent lamps, and in a lesser quantity in day light. They cause, for example, the yellowing of artworks exposed.
Mold
The mold which is able
to grow on artworks is fungus and bacteria. Those organisms feed
themselves from materials that they damage. Bacteria are capable of
degrading many materials by modifying and weakening them. Most of the
molds are developing between 4 and 30°C, and only when relative humidity
exceeds 60%. Degradations observed are the appearance of indelible
stains of various colours and a weakening of the paper, until sometimes
its complete destruction.
Insects
Some conditions are
favourable to the developpment of insects. In order to eat, they are
attacking objects or documents containing cellulose. High temperature
and humidity, bad ventilation, insufficient and irregular cleaning,
presence of food, bad tightness of doors and windows, bad state of the
building and the entrance of contaminated objects in the environment are
the main causes of insects development. Degradations caused by insects
are progressive and can go from simple holes til total destruction of
the artwork. Insects use organic materials to nourish themselves and to
nest. They cause physical damages when they deposit their eggs
(galleries) and chemical damages when their larvae are growing up. The
latters secrets substances which degrade organic material in order to
make it eatable.
